The cross sections for the processes $\gamma \nu \to \gamma \gamma \nu$, $\gamma \gamma \to \gamma \nu \overline{\nu }$, and $\nu \overline{\nu }\to \gamma \gamma \gamma$ are calculated with the aid of an effective Lagrangian derived from the standard model. These cross sections are shown to be much larger than the elastic cross section $\sigma (\gamma \nu \to \gamma \nu )$ for photon energies $\omega >1\mathrm{}\mathrm{keV}$. Possible astrophysical implications are discussed.

• Received 27 February 1997

DOI:https://doi.org/10.1103/PhysRevLett.79.569